Increasing awareness of the undesirable effects of industrially generated and emitted coal combustion products (flue gas), has led to a corresponding need to treat these gases so as to remove the pernicious components or convert them to harmless (and often useful) products. The industrial flue gases with which the present invention is especially concerned are those produced by coal-fired boilers as are commonly employed in electric utility installations. Among the relatively pernicious flue gases of concern produced by these boilers are sulfur dioxide (SO2) and other pollutants (e.g., hydrochloric acid, hydrofluoric acid, sulfuric acid, mercury, selenium, and other trace constituents). These pollutants have for many years been removed from industrial flue gases by “scrubbing” the flue gas with lime/limestone slurries or the like, most commonly in some type of vessel in which the flue gas is contacted with a counter-current flowing stream of the mentioned slurry. Such methodology can and is used in the large newer boiler installations found in many utility operations. However there also exist in the electric utility industry a large number of older, coal-fired boilers, which presently include no flue gas scrubbers, and thus are urgently in need of some instrumentality to remedy their continuing polluting emissions. Typically an overall SO2 removal efficiency of 80% to 99% is desirable, but the costs of installing or retrofitting equipment capable of such results has in the past been very high, and therefore has tended to discourage the purchase and installation of what otherwise would be most desirable enhancements. The present invention has as one of its key objects to provide a system which will remedy such reluctance by virtue of producing outstanding results at what are comparatively modest costs which may also extend the useful life of the older, boilers rather than retiring them as an alternative to retrofitting more expensive FGD systems.